Tracking the Prevalence of FAS.

Surveillance programs allow the tracking of the prevalence of a condition over time. Tracking the prevalence of FAS poses particular problems, however, as there is no "gold standard" of diagnosis. To evaluate the effectiveness of prevention efforts, surveillance techniques must be refined.

F etal alcohol syndrome (FAS) is a birth defect that causes significant lifetime disabilities (Abel 1990). But unlike many other birth de fects, FAS, which is caused by maternal alcohol abuse during pregnancy, is pre ventable (Abel 1990). In fact, prevention of FAS is a national health priority included in the Healthy People 2000 objectives for health promotion and disease prevention (U.S. Department of Health and Human Services 1990 [USDHHS]). The specific health objective is to reduce the rate of FAS to no more than 1.2 cases per 10,000 live births by the year 2000.
Baseline data for this objective were derived from a national hospitalbased epidemiologic surveillance program of birth defects-the Birth Defects Monitor ing Program (BDMP) of the Centers for Disease Control and Prevention (CDC). Although the rate of 5.2 cases per 10,000 live births in 1992 seems to be an increase over the baseline rate of 2.2 cases per 10,000 (USDHHS 1990), it more likely represents improvements over recent years in recognition and reporting of FAS at birth.
In this article, we review the chal lenges of developing simple and efficient Statebased and national epidemiologic surveillance that can track what progress is being made toward meeting the Healthy People 2000 objective for FAS.

EPIDEMIOLOGIC SURVEILLANCE
CDC defines epidemiologic surveillance as the ongoing systematic collection, analysis, and interpretation of health data that are essential to the planning, imple mentation, and evaluation of public health practice (Thacker et al. 1989). Such sur veillance is closely integrated with timely dissemination of these data to anyone who requires this information. To monitor progress in meeting the FAS prevention objective, epidemiologic surveillance is needed to evaluate changes in the rate of FAS over time.

Methodological Problems
Diagnosing FAS. Developing surveil lance of FAS presents unique challenges. Because there is no simple, objective laboratory test for diagnosing FAS, diag nosis is based primarily on clinical defini tions developed for the purpose of clinical practice and research (Sokol and Clarren 1989). To meet the clinical FAS case def inition, the patient must exhibit symptoms in each of the following three categories: (1) prenatal or postnatal growth retarda tion; (2) central nervous system abnor malities; and (3) characteristic abnormal facial features (dysmorphology), includ ing short palpebral fissures (eye open ings), an elongated midface, a long and flattened philtrum (area between the nose and mouth), and a thin upper lip (see the photograph on p. 13, in the article by Becker et al.). It is also helpful to deter mine if the patient was exposed prenatally to alcohol, but diagnosis can still be made if such information is unavailable (Sokol and Clarren 1989).
Applying these diagnostic criteria requires expertise in recognizing dysmor phic features. Moreover, the clinical fea tures of a child with FAS may change with age (Streissguth et al. 1991; see the article by Streissguth,. There is encouraging evidence that the clinical recognition and reporting of FAS is im proving (CDC 1993a). However, such improvements may prove troublesome by clouding the true changes in the rate of FAS over time.
Collecting Data. CDC includes FAS in its two birthdefects surveillance programs. The first program is the BDMP, which relies on reported hospital discharge diag noses of newborns that use the Inter national Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) (World Health Organization 1989). This program started monitoring FAS after 1979 when the ICD-9 introduced a code (760.71) that could be applied to the syndrome.
The second program is the Metropol itan Atlanta Congenital Defects Program (MACDP) (Lynberg et al. 1990), which started in 1968 and is the oldest active caseascertainment birthdefects surveil lance program in the United States. It monitors all births occurring in the five county metropolitan Atlanta area-current ly about 38,000 per year. The MACDP, unlike the BDMP, uses multiple sources to identify diagnoses of FAS in newborns and infants, including obstetrical, nursery, and pediatric logs. In addition, the MACDP identifies cases of FAS diagnosed through the first year of life, not solely at birth.
Because the BDMP, the MACDP, and other birthdefects surveillance programs examine only the medical records rather than the children directly, they rely on clinicians recognizing the condition and recording the diagnosis in the patient's medical record. Further, the BDMP relies on the diagnosis of FAS during the new born's hospital admission and the record ing of that diagnosis in the baby's discharge record. The MACDP, on the other hand, detects diagnoses mentioned anywhere in a medical record, throughout the first year of a child's life.

DESIGNING A SURVEILLANCE PROGRAM
Three important attributes of a successful surveillance program are sensitivity, predicted value positive, and representa tiveness (Klaucke 1992). These are de fined and discussed below.

Sensitivity of Surveillance
Sensitivity is a measure of how well the surveillance program detects cases of a condition. The greater the percentage of cases identified, the greater the chance to identify true changes in the rate of the condition over time.

Underdiagnosis.
A case definition that only captures some of the FAS cases will decrease the surveillance program's sensi tivity. Sensitivity also will be decreased when surveillance is based only on clini cal recognition of FAS, because the con dition may sometimes be hard to discern. For example, the facial features that are characteristic of FAS can be missed by clinicians who may not be familiar with dysmorphology (Morse et al. 1992).
During a 6year period, a separate longitudinal study examined prenatal exposure to alcohol in a large metropoli tan hospital in Atlanta ). The study examined babies born at the hospital between 1980 and 1986, using a systematic checklist specific to the features of FAS. The concurrence of the study and the MACDP surveillance program allowed a comparison of their rates of diagnosis. Only 38 percent of the FAS cases diagnosed by the longitudinal study also were diagnosed by the MACDP ). This may indicate a lack of clinical recognition, a failure to record findings in the medical record, the use of variable criteria for the case defini tion, or a combination of all of these by the MACDP program.

Underreporting of Diagnosis.
Another potential bias is that FAS may be recog nized and recorded in medical records at different rates in different populations. About 75 percent of all recorded cases of FAS in the MACDP came from a large innercity hospital that serves the poor and uninsured. Between 1975 and 1989, the innercity hospital reported 88 FAS cases out of 98,000 births, whereas a comparable large suburban hospital reported 3 cases out of 72,000 births over the same period. Although it is possible that the rate of FAS in the two hospitals truly is different, lack of recognition of FAS, not recording the diagnosis, and bias in suspecting diagnosis should be evaluated as potential reasons for the difference.
In another study, which looked at the rate of diagnosis of FAS by pediatricians, a survey in Massachusetts found that among pediatricians who reported ever making a diagnosis of FAS, 9 percent also reported not recording the diagnosis in the medical record (Morse et al. 1992). The reasons for not recording the diagnosis were not explored. Regardless of whether the diagnosis is missed or not recorded, both events decrease the sensitivity of FAS surveillance and therefore will cause the underestimation of the rate of FAS.
Using a Limited Population. The child's age when the diagnosis of FAS is made also may affect the sensitivity of the surveillance program. Surveillance of FAS based on newborn diagnosis will likely have a low sensitivity, because some affected newborns may have subtle facial abnormalities, inapparent central nervous system deficits, and normal birth weight (Abel and Sokol 1991). In addi tion, clinical, behavioral, and facial fea tures may vary with the age of the child beyond the newborn period (Streissguth et al. 1985). In the MACDP, about 78 per cent of the FAS cases were diagnosed during the newborn period (unpublished data). Surveillance programs that focus on the diagnosis of FAS at a specific age may tend to have lower sensitivity than others that cover all age groups.
In summary, several factors will affect the sensitivity of FAS surveillance. They include underdiagnosis, lack of recording of the diagnosis in the medical record, the possibility of stereotyping populations, inclusion of a limited population subset, and a restrictive case definition.

Predictive Value Positive
A good surveillance program for FAS must identify the rate of true cases of FAS. Each case recorded using the sur veillance case definition should have a high probability of being a true case of FAS. Predictive value positive (PVP) is the measure of how accurately cases are diagnosed given the nature of the case definition. FAS presents a particularly challenging situation for estimating PVP because there is no known "gold stand ard" for diagnosis. Even knowledgeable dysmorphologists often disagree about clinical diagnoses of FAS.

Low PVP.
A case definition that allows inclusion of noncases will decrease the PVP of the surveillance. For example, if an FAS surveillance program uses a case definition of intrauterine growth retarda tion and a history of maternal alcohol abuse only but not the dysmorphic facial features, it is likely that many cases in cluded under that definition may not meet the clinical criteria of FAS.
Clinical features in each of the three categories of the current case definition are not unique to FAS; they may result from many different causes. For exam ple, the general definition of intrauterine growth retardation is weight and length below the 10th percentile for gestational  1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 Year of Birth  , 1979-1992. age. Using this definition, about 10 percent of all newborns would meet this criterion, most of whom will not have FAS.
High PVP. Selecting a case definition that has a high PVP may decrease the sensitivity of the surveillance program. One can develop a definition for a condi tion that has such a high PVP that there is little doubt that each recorded case is a true case of the condition. Such a specific definition, however, also may miss many true cases, thereby greatly lowering the program's sensitivity. An example of this dilemma is a report of the sensitivity and PVP of isotretinoin embryopathy, or birth defects caused by maternal use of retinoic acid. The case definition with the highest PVP had a sensitivity of only about 16 percent (i.e., 84 percent of all true cases were missed) (Lynberg et al. 1990). However, the case definition avoided counting false cases. If the intent of the surveillance is to follow the trends of a condition, without trying to ascertain its incidence, such an approach may be adequate. In the situation of FAS, however, determining the incidence is quite important, given the current Healthy People 2000 objective and the potential use of the surveillance as a registry that may track access of services to affected children.

Representativeness
Representativeness is the ability of the surveillance program to reflect accurately the occurrence of the condition over time in the population of interest.
A major purpose of FAS surveillance on a national level is to gauge the trends in the U.S. population. Representative ness ensures that the picture painted by the surveillance program reflects the picture of the Nation. For example, using data from the BDMP, Chávez and col leagues (1988) found that the reported rate of FAS varies by race and ethnic group. If the surveillance is not popula tion based, as with the case of the BDMP, and the racial and ethnic distribution does not reflect that of the general population, the findings may not be generalized ex cept with appropriate adjustments.
The rate of FAS in a population is dependent on the rate of maternal alcohol abuse during pregnancy. If a specific sub population included in the surveillance program has a rate of alcohol abuse dur ing pregnancy different from that of the general population, the representativeness of the surveillance also will be affected. Stereotyping that affects the program's definition or diagnosis of FAS also can affect representativeness.

The Estimates
The estimated birth prevalence of FAS among newborns identified through the BDMP increased from about 1 case per 10,000 live births in 1979 to 5.2 cases per 10,000 live births in 1992 (figure 1) (CDC 1993a). As mentioned above, the BDMP is based on doctors recording the ICD-9-CM FAS diagnosis code at dis charge from the hospital of birth, and the program has not been evaluated in terms of its sensitivity and PVP. In 1992, the MACDP reported a rate of 3.3 cases per 10,000 live births. Both programs crudely estimate the average incidence of FAS for the reporting period 1979-1992 as 2 cases per 10,000 live births (Lynberg and Edmonds 1992). It is difficult to tell whether the reported increase during the last decade represents a true increase or the increased awareness and improved reporting among health care profession als. Interestingly, Serdula and colleagues (1991) reported that between 1985 and 1988, the percentage of women who drank during pregnancy actually declined. However, this decline was not evident for less educated women and women under age 25 years. Abel and Sokol (1991) 1 estimated the rate of FAS to be 3.3 cases per 10,000 live births. This estimate is based on the results of 15 prospective studies and 4 surveillance studies from Australia, New Zealand, Swe den, the United Kingdom, and the United States (Abel and Sokol 1991). None of these studies was population based.

Limitations of the Estimates
Potential limitations of the CDC data sources include decreased sensitivity arising from decreased recognition of FAS in newborns (CDC 1993a), possible failure to incorporate the FAS diagnosis into the medical records (CDC 1993b), and the possible inappropriate use of the ICD-9-CM FAS code for reporting pre natal exposure to alcohol. The MACDP and the BDMP were designed primarily to monitor major birth defects in infants-to identify structural birth defects that are evident at birth or have significant clinical manifestations during the first year of life. They were not designed to track syn dromes such as FAS that have few major birth defects.
In their estimate, Abel and Sokol (1991) did not use data that were population based, and they did not include minorities, Native Americans in particular. This omission may underestimate the rate of FAS. A recent survey of FAS among Native Alaskans reported an FAS rate of 21 cases per 10,000 live births (CDC 1993b).

IMPROVING FAS SURVEILLANCE
Given the limitations of current national FAS surveillance, researchers must im prove it by systematically determining the strengths and shortcomings of existing surveillance, for example, through evalua 1 An earlier study of Abel and Sokol (1987) that surveyed 19 published epidemiologic studies world wide reported an overall rate from all studies of 1.9 cases of FAS per 1,000 live births (i.e., 19 cases per 10,000 live births). tion of the sensitivity, PVP, and represen tativeness of these existing programs. In addition to improving the national surveil lance program, researchers should focus attention on Statebased FAS surveil lance. The proportion of hospitals partici pating in the BDMP is declining, and participation in some States is insufficient to estimate rates of FAS for these States.
The first task in improving surveillance is to develop a uniform case definition of FAS that optimally balances sensitivity with precision and can be used for surveil lance. This should be followed by uniform ity in application of the case definition. Also, the development of sensitive and specific screening instruments, including biologic markers, could contribute greatly to better epidemiologic data in this field. The second task is to ensure uniformity in methods of reporting data and in surveil lance programs to receive the data. The combined effort of all concerned with the prevention of FAS will help make im proved surveillance of FAS a reality. ■